This project will use a combination of genetic and biochemical methods to investigate the plasma-membrane [H+]-ATPase of Neurospora crassa. Existing evidence indicates that the ATPase functions as an electrogenic proton pump and that, in having a single Mr = 104,000 polypeptide subunit, it is structurally related to the transport ATPases of animal cells. Experiments will be carried out to clone the ATPase gene in order to learn the complete amino acid sequence of the Mr = 104,000 polypeptide. The biogenesis of the polypeptide will be studied and--by means of mutant isolation, modification with group-specific reagents, and monoclonal antibodies--the relationship between protein structure and function will be explored. The results will provide insight into the molecular mechanism of this primary fungal transport system and, at the same time, will pave the way for a detailed comparison between the fungal ATPase and the [Na+, K+]-, [Ca++]-, and [H+, K+]-ATPases of animal cells.